Biomass allocation in three macrophyte species in relation to the disturbance level of their habitat

1. The hypothesis was tested that perennial plants surviving in habitats frequently disturbed by floods should demonstrate the ability to escape the frequently scoured surficial zone by using refugia located deeper in the substrate. As a consequence, they should allocate more biomass to their underground parts than when growing in rarely disturbed habitats.
2. The allocation of biomass of three aquatic macrophytes ( Berula erecta , Groenlandia densa , Myriophyllum spicatum ) to their different organs (underground and above-ground parts) was measured in former river channels organized along a gradient of scouring flood disturbances.
3. For each species, biomass allocation to underground parts varied between sites: from 10.2 to 37.5% in B. erecta , from 14.9 to 31.1% in G. densa and from 8.4 to 23.2% in M. spicatum . It was correlated to the flood disturbance level of the site for B. erecta and M. spicatum but not for G. densa. No relationship was found between biomass allocation to underground parts and sediment richness.
4. The plasticity in biomass allocation of these three macrophyte species appears to be an adaptation to the variability in environmental conditions and implies difficulties in the classification of plant primary strategies, when this type of plasticity is ignored.